This invention relates to the manufacture of batteries comprised of a plurality of interconnected individual electrochemical calls.
Rechargeable electrochemical batteries include two or more electrochemically independent cells that are connected together in series to provide a battery output voltage that is a multiple of the voltage of each individual cell. In the familiar automobile battery, these cells are contained in an acid-resistant casing and all connections between cells are made internally of this casing. In a battery of this type, each cell does not exist independently as a unit but, rather, is found only as one of a series of components embodied in the battery.
In many other types of battery applications, however, the battery is comprised of a plurality of interconnected individual cells, each of which is by itself a finished product. In batteries of this type, the individual cells, which can take the form of the familiar D-size flashlight cells, are placed side by side or end to end, and interconnected by one means or another in order to raise the battery potential. There are several advantages to this type of battery, not the least of which is the fact that a defective individual cell in the battery can be replaced without destroying the entire battery. Another advantage is the versatility which is possible, since batteries of any electrical capacity and voltage can be constructed simply by altering the number and type of individual cells used in the battery. In the case of sealed lead acid cells, each has a nominal circuit voltage of between about 2.1 volts and 2.2 volts. Because of standardization in the industry, it is generally found that lead acid battery cells are interconnected in threes so as to obtain battery voltages in multiples of six volts. A six-volt battery is thus arrived at by interconnecting three cells (3.times.2 volts=6 volts), a twelve-volt battery by interconnecting six cells (6.times.2-12 volts).
It is highly desirable, and often necessary, that the interconnections between cells be relatively permanent and not subject to vibration, oxidation and other effects which impair the integrity of the conductive connection between adjacent cells or which appreciably alter the inter-cell electrical resistance. For that reason, small-scale batteries usually have employed permanently welded connections between cells. A welded connection offers permanence and reliability; yet, it can also be separated when necessary by stripping the welded conductor from the terminal.
The cells themselves usually comprise a cylindrical casing having projecting from the top surface thereof a pair of spade terminals, these terminals being relatively thin, flat conductors which are adapted to receive spade connectors. For welding purposes, however, it is not convenient to have the terminals projecting upwardly from the cell, as this makes it difficult to effect a weld between the terminal and the interconnecting conductor. Moreover, leaving the terminals in the upstanding position would add materially to the dimensions of the battery and tend to establish loops in the connecting links. It is accordingly the usual practice to bend over the projecting terminals so that they lie generally in a common plane, place a conductive link over the exposed surfaces of the bent terminals, and then weld the conductive link to the terminals.
The terminal bending operation is generally carried out on the cell by an operator who simply folds over the terminals by hand. Similarly, the placement of the interconnecting link over the terminals and the welding step is also done by hand, it being understood that the operator places the cell or cells into the appropriate position of a welding apparatus to effect the latter step. The cells sometimes are held together with an adhesive strip which is placed on the cells being interconnected, again this strip being carried out by hand.
The extensive hand work required to interconnect cells in the manner just described results in the expenditure of excessive operative time, and subjects the cells to variations in quality inherent in any hand operation. For example, it is difficult for a human operator to bend the terminal tabs in a consistent manner from one cell to the next. The terminals tend to bend at different distances above the top surface of the cell and thus do not always lie in a common plane. Equal difficulty is encountered in attempting to bend the terminals over consistently along the same bend line. Adding to these variations is the frequent misalignment of the link relative to the terminal, a condition which can contribute to improper welding and insufficient weld strength.